A large number of knitting needles are arranged in the needle beds of a flat knitting machine in a state of being contained in needle grooves slidably back and forth. Knitting needles selected by a selector actuator according to knitting data are forward and backward operated by a group of cams mounted on a carriage that reciprocates over the needle beds, so that the flat knitting machine can knit fabrics having a jacquard pattern, a design pattern, etc.
For example, as described in Japanese Published Unexamined Patent Application Publication No. H5-321102 and Japanese Published Unexamined Patent Application No. H9-241952, a device using a fixed electromagnet is known as a needle-selecting means for selecting knitting needles that are forward and backward operated. A device using a fixed electromagnet can select needles at a high speed and has fewer troubles during knitting because a selector actuator is fixed.
The fixed electromagnet of the selector actuator can be classified into two types one of which is a current-application hold type that is adsorbed to an end of a desired selector by applying an electric current to the coil of a pole from a power supply control unit and the other of which is a current-application release type that releases the adsorption of an end of a desired selector by applying an electric current to the coil of the pole from the power supply control unit. The needle selection device of the current-application release type has an advantage, for example, in enabling easy handling at the time of a power failure or at the time of power recovery after a power failure.
A carriage is provided with a selector actuator made up of a permanent magnet and an electromagnet excited by being supplied with electric power from the power supply control unit. This selector actuator selects desired needles by adsorbing the selector by means of the permanent magnet, by canceling the magnetic flux of the permanent magnet by use of the magnetic flux of the electromagnet excited by the current supplied from the power supply control unit, and by undoing the adsorption of the selector.
In this magnetic-type needle selection device, a current-application interval from the start of current application by which the electromagnet is actuated to the end thereof is set at a predetermined interval, for example, at ½ of a gauge pitch.
In more detail, detecting elements “A” and “B” that detect the selector have been conventionally provided in order to detect a power-supply starting position and a power-supply stopping position, for example, as shown in FIG. 6. The distance between knitting needles is detected as four positions “a” to “d” as shown in FIG. 7A and FIG. 7B by turning the detecting elements “A” and “B” on and off. Based on the detection of these four positions, the power-supply starting position E1 and the power-supply stopping position E2 are controlled so that the power supply (i.e., current application) is started at, for example, position “b” is stopped at position “d.”
After a predetermined rise time S elapses, a desired magnetic flux G is generated in the electromagnet as shown in FIG. 7 by being supplied with an electric current from the power supply means as mentioned above.
In the magnetic-type needle selection device, a positional coincidence is established between the center PC of a current-application interval P determined by the power-supply starting point “b” and the power-supply stopping point “d” and the center WC in the width direction W of a selector to be selected when the carriage moves at a general moving speed (see FIG. 6).
The flat knitting machine knits fabrics while reciprocating the carriage over needle beds. At this time, the carriage is repeatedly accelerated and decelerated by its reversals, so that the moving speed of the carriage in one course is not always constant. Not only when the carriage is reversed but also when the carriage is midway in the course, cases occur in which the moving speed of the carriage is changed.
As in the conventional magnetic-type needle selection device, a current-application interval from the start of a power supply operation by which the electromagnet is actuated to the end thereof is set at, for example, ½ of the gauge pitch of the flat knitting machine. Therefore, a knitting machine having a coarse gauge can cope with a change in moving speed of the carriage with a relatively large margin. On the other hand, a knitting machine having a fine gauge has a current-application interval P1 shortened as shown in FIG. 5A and FIG. 5B. As a result, the period of time of an F portion that effectively acts on a selector selected by the electromagnet (i.e., the period of time of a flat portion obtained by subtracting a rise time S from a current-application interval P in the figures) becomes short, and, in addition, the rise time S of a magnetic flux generated in the electromagnet by the power supply means is substantially constant regardless of the moving speed of the carriage. Hence, the F portion is dislocated toward the upper side in the moving direction of the carriage from the center of a selector to be selected.
Therefore, in a fine-gauge knitting machine having twelve or more gauges, the magnetic flux of the electromagnet rises late when the carriage moves at a high speed. On the other hand, when the carriage moves at a low speed, if the power-supply starting point of time is early, magnetism affects a next selector on the forward side, and, if the power-supply stopping point of time is late, residual magnetism affects the following selector. Therefore, disadvantageously, an error in selecting needles is liable to occur.
The aforementioned problem also arises when the knitting machine is cooled so that the viscosity of a lubricant becomes high and when adhesion of dust or the like makes the movement of the selector slow.
Additionally, disadvantageously, if dimensional errors or assembly errors of related components exist in the fine-gauge knitting machine, the knitting machine cannot cope with a change in moving speed of the carriage as in the aforementioned case, and much time will be taken to adjust it.